5.6 Transmission Order of the Parameters

   


The parameters are transmitted sequentially as a block consisting of an integer number of octets. The order of transmission of the parameters from the tree structure is shown in Figure 5.6. First the NPar(1) and SPar(1) parameters are passed, followed by the NPar(2) and SPar(2) subparameters. For each SPar(2), all corresponding NPar(3) subparameters must be passed.

Figure 5.6. Transmission order of the parameters.

graphics/05fig06.gif

In Figure 5.6 we show there to be N level 2 parameters, which are the sub parameters to first level SPar set. Par(2) j corresponds to the set (block) of Level 2 parameters associated with the j th Level 1 SPar, which may contain NPars and SPars. For each second level SPar, there are a set of third-level subparameter blocks labeled NPar(3) j,k , where k would range from 1 to M and the value of M would be different for each second-level SPar set (i.e., for each value of j). Transmission begins with the first octet of the NPar(1) set and ends with the last octet of the Par(2) N set. For each Par(2) set [i.e., Par(2) j ], transmission begins with the first octet of NPar(2) j and ends with the last octet in NPar(3) j,M .

In order to determine the beginning and end of a parameter block, we need to define a set of delimiting rules. Following are the delimiting rules adopted in G.994.1.

In each octet of a parameter block, at least one bit is defined as a delimiter bit, which defines the last bit to be transmitted in the block. A logic 0 in the delimiter bit position indicates that there is at least one additional octet in the block to be transmitted; a logic 1 in the delimiter bit position indicates the last octet in the block to be transmitted.

For the NPar(1), SPar(1), and all of the Par(2) blocks, bit 8 is used as a delimiter bit, and the remaining bits are used to encode the parameter data. For the above parsing rule to work properly, the identification (I) and standard information (S) fields each need to include at least one NPar(1) octet and one SPar(1) octet. As shown in Figure 5.6, there are N Par(2) blocks that correspond to the SPar(1) block. The delimiting bit is shown as an x in the bit #8 position.

For each Par(2) block, bit 7 serves as the delimiter bit in the corresponding NPar(2) block, Spar(2) block, and each of the associated NPar(3) blocks. The illustration in Figure 5.6 shows there to be M of the NPar(3) blocks for each SPar(2) block, where the value of M may be different for each SPar(2) block. The delimiting bits are shown with an x in the bit #8 and #7 positions .

Note that each Par(2) block may transmit both NPar(2) and SPar(2) blocks or only NPar(2) blocks. If only NPar(2) block is transmitted, the final octet in the block will contain a logic 1 in each delimiter bit position.

In order to be compatible with future versions of G.994.1, a receiver needs to parse all parameter blocks and ignore information that is not understood .


   
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DSL Advances
DSL Advances
ISBN: 0130938106
EAN: 2147483647
Year: 2002
Pages: 154

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